State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China; University of the Chinese Academy of Sciences, Beijing 10049, China.
State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China.
Sci Total Environ. 2019 Feb 10;650(Pt 1):303-312. doi: 10.1016/j.scitotenv.2018.09.038. Epub 2018 Sep 4.
Anthropogenic activities have substantially increased soil nutrient availability, which in turn affects ecosystem processes and functions, especially in nutrient-limited ecosystems such as alpine grasslands. Although considerable efforts have been devoted to understanding the responses of plant productivity and community composition to nitrogen (N) and phosphorus (P) enrichment, the nutrient enrichment effects on soil organic carbon (SOC) and microbial functions are not well understood. A four-year field experiment was established to evaluate the influence of continuous N and P enrichment on plant growth and SOC content in an alpine grassland of the Qinghai-Tibetan Plateau. The study included four treatments: Control without addition, N addition, P addition, and N plus P addition. N addition strongly increased aboveground plant biomass and decreased species richness by promoting growth of the dominant grasses species. In contrast, N and P enrichment significantly decreased SOC, especially the recalcitrant organic C content in the surface layer (0-10 cm) by reducing the slow C pool and enlarging the active C pool. Microbial biomass and activities of C-degrading enzymes (β-glucosidase, cellulase and polyphenol oxidase) and an N-degrading enzyme (chitinase) increased with nutrient inputs. The CO emissions during a 300 d incubation period were positively correlated with the cellulase and chitinase activities, while the slow C pool was negatively correlated with the cellulase and polyphenol oxidase activities. Consequently, N and P enrichment accelerated decomposition of the recalcitrant C by stimulating microbial growth and increasing enzyme activities, leading to negative impacts on soil C sequestration. Overall, the results indicate that alpine grassland soils of the Qinghai-Tibetan Plateau may be changing from a C sink to a C source under increasing N and P availability, and improvement of alpine grassland management through nutrient inputs should consider not only the aboveground biomass for grazing, but also the soil C sequestration and ecosystem functioning.
人为活动大大增加了土壤养分的有效性，这反过来又影响了生态系统过程和功能，特别是在养分有限的生态系统中，如高山草原。尽管人们已经付出了相当大的努力来理解植物生产力和群落组成对氮（N）和磷（P）富集的响应，但对土壤有机碳（SOC）和微生物功能的养分富集效应还了解甚少。为了评估连续氮和磷富集对青藏高原高山草原植物生长和 SOC 含量的影响，进行了为期四年的野外实验。该研究包括四个处理：不添加对照、氮添加、磷添加和氮加磷添加。氮添加通过促进优势草种的生长强烈增加了地上植物生物量，并降低了物种丰富度。相比之下，氮和磷的富集显著降低了 SOC，特别是通过减少缓慢 C 库和扩大活性 C 库，降低了表层（0-10 cm）的难降解有机 C 含量。微生物生物量和 C 降解酶（β-葡萄糖苷酶、纤维素酶和多酚氧化酶）以及 N 降解酶（几丁质酶）的活性随着养分输入而增加。在 300 d 的培养期内，CO 排放与纤维素酶和几丁质酶活性呈正相关，而缓慢 C 库与纤维素酶和多酚氧化酶活性呈负相关。因此，氮和磷的富集通过刺激微生物生长和增加酶活性加速了难降解 C 的分解，从而对土壤 C 固存产生负面影响。总的来说，这些结果表明，在青藏高原高山草原土壤中，随着氮和磷供应的增加，土壤可能正在从 C 汇转变为 C 源，通过养分输入改善高山草原管理不仅应考虑用于放牧的地上生物量，还应考虑土壤 C 固存和生态系统功能。
